To determine if parasympathetic control of gastric emptying differs between obese and lean subjects, 6 lean and 6 obese subjects underwent 2 experimental conditions administered in a counter-balanced order: 1) saline infustion and 2) atropine infusion (0.4 mg/m2bolus; 0.4 mg/m2/hr) for 2 hours. Subjects ingested a 600 kcal meal (64% carbohydrate, 23% fat, 13% protein) composed of orange juice, an egg sandwich cereal, milk and banana. The juice was labeled with indium-111 and the sandwich was labeled with Technicium-99m to monitor emptying of liquid and solid food, respectively. After meal ingestion, subjects lay supine. Anterior and posterior images were taken every 90 sec for a total of 90 min. No significant differences in liquid or solid emptying were found between groups during the saline conditionatropine significantly slowed gastric emptying of liquid (F=20.5, P<0.002) and solid food (F=15.1, P<0.05, in both groups. In obese subjects, both liquid and solid food were retained to a greater extent following atropine compared with lean (liquid: 100% vs 57%, P<0.02: solid: 74% vs 33%, p<0.05, obese, lean). These data suggest that there is greater tonic vagal efferent activity contributing to the rate of gastric emptying in the obese.